From 5b3ea51f7bcb74d55e7f37356bc0ca823aa2e602 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Tue, 22 Jun 2021 16:39:56 +0200
Subject: [PATCH] drm: disable all CRTCs on startup

If the CRTC we've selected is being used on another connector,
our modeset fails.
---
 src/drm.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/drm.cpp b/src/drm.cpp
index b63f5b1..52dea66 100644
--- a/src/drm.cpp
+++ b/src/drm.cpp
@@ -463,6 +463,14 @@ int init_drm(struct drm_t *drm, const char *device, const char *mode_str, unsign
 		}
 	}
 
+	// Disable all CRTCs. This ensures the CRTC we've selected isn't being used
+	// by another connector.
+	for (i = 0; i < resources->count_crtcs; i++) {
+		ret = drmModeSetCrtc(drm->fd, resources->crtcs[i], 0, 0, 0, nullptr, 0, nullptr);
+		if (ret != 0)
+			fprintf(stderr, "failed to disable CRTC %" PRIu32 ": %s", resources->crtcs[i], strerror(-ret));
+	}
+
 	drmModeFreeResources(resources);
 
 	drm->connector_id = connector->connector_id;